The themes add a cartoonish backdrop to the top of the page and tweak text and border colors to match. What's more, they're dynamic, meaning they change depending on the time of day. Alas, the background below the header remains as stark and white as ever, and you can't make custom changes to any of the themes. Even so, it's good to see Google finally giving the homepage a little window dressing. It's been too drab for too long.